The Type 97 medium tank Chi-Ha was a medium tank used by the Imperial Japanese Army during the Second Sino-Japanese War, at Nomonhan against the Soviet Union, and the Second World War. It was the most widely-produced Japanese medium tank of WWII, with about 26mm thick armor on its turret sides, and 33mm on its gun shield, considered average protection in the 1930s. The 57mm main gun was a carry over from the 1933 Type 89 medium tank, and was designed to support the infantry, while the 170 hp diesel Mitsubishi was a capable engine for the tank in 1938. But was less effective after 1941 than most Allied tank designs.The Type 97's low silhouette, asymmetric turret, semicircular radio aerial on the turret roof, complicated hull front, and seesaw-type suspension system combined to give the tank a unique appearance that distinguished it from other contemporary Japanese tanks. The suspension was derived from the Type 95 light tank, but used six road wheels instead of the Type 95's four road wheels.The Tokyo factory of Mitsubishi Heavy Industries completed an experimental vehicle designated Chi-Ha and the Army's Osaka Arsenal completed the Chi-Ni. Chi came from Chusen-Sha ("Medium Tank"). Ha and Ni equate to "C" and "D" in Japanese army nomenclature, making the Chi-Ha the "Medium Tank Model 3," and Chi-Ni the "Medium tank Model 4." Although the requirement was for a 47 mm cannon, both prototypes used the same short-barreled 57 mm cannon as used by the Type 89B. The Osaka Arsenal Chi-Ni was 9.8 metric tons, attained 30 km/h and had a one-man turret and 25 mm armor. The more expensive Mitsubishi Chi-Ha was 13.5 metric tons, attained 35 km/h and had a two-man turret and 33 mm armor on the turret front, 22 mm on the hull front, but only 9 mm on the hull sides.